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COMPARISON OF TIME-OF-FLIGHT AND DOUBLE FOCUSING MASS SPECTROMETRY FOR REACHING TENTATIVE IDENTIFICATIONS FOR UNANTICIPATED COMPOUNDS ADDED TO DRINKING WATER BY TERRORISTS
Citation:
Grange, A H., F. A. Genicola, AND G W. Sovocool. COMPARISON OF TIME-OF-FLIGHT AND DOUBLE FOCUSING MASS SPECTROMETRY FOR REACHING TENTATIVE IDENTIFICATIONS FOR UNANTICIPATED COMPOUNDS ADDED TO DRINKING WATER BY TERRORISTS. Presented at Annual American Society of Mass Spectrometry meeting, Orlando, FL, June 2-6, 2002.
Impact/Purpose:
Provide state-of-the-science sampling, analysis, separation, and detection methods to allow rapid, accurate field and laboratory analyses of contaminated soils, sediments, biota, and groundwater to support Superfund clean-up decisions. Apply state-of-the-science methods in chemical analysis and data interpretation (e.g., mass spectral interpretation) to actual problems of OSWER, the Regions, and the States, in cooperation with the Las Vegas Technical Support Center as well as by direct contacts with Regional and State employees. Provide technical advice and guidance to OSWER using the environmental chemistry expertise (e.g., mass spectrometry, analytical methods development, clean-up methodology, inorganics, organometallics, volatile organics, non-volatile organics, semi-volatile organics, separation technologies, etc.) found within the branch.
Technical research support for various projects initiated either by Regions/Program Offices or ECB scientists. While these efforts will support the Regions and Program Offices, they cannot be predicted or planned in advance, and may serve multiple duty (e.g., solve real-world problems, serve to ground-truth analytical approaches that ECB is developing, transfer new technology). Many of the activities in this task support requests involving enforcement decisions and therefore are categorized as "environmental forensics".
Description:
Local monitoring of post-treatment drinking water using bench-top mass spectrometers could identify target compounds in a mass spectral library. However, a terrorist might seek to incite greater hysteria by injecting or infusing a mixture of unanticipated compounds of unknown toxicity. GC/MS using time-of-flight (TOF) and double focusing mass spectrometry will be compared for reaching tentative identifications of two compounds that were found in drinking water, but not found in mass spectral libraries. Recent articles demonstrate 5-10 ppm error limits for exact mass determinations made using TOF mass spectrometry for ions produced from compounds introduced into the mass spectrometer by chromatographic techniques. These exact masses provide confirmatory evidence for target compound identities, but seldom correlate to unique elemental compositions.
METHODS
Determination of the exact masses of the +1 and +2 mass peak profiles and their abundances relative to the monoisotopic ion provide four additional measurements for rejecting incorrect compositions that are possible based on the exact mass of an ion and the error limits of its measurement. These values are obtained from mass peak profiles plotted from selected ion recording data (MPPSIRD) acquired as compounds elute into a double focusing mass spectrometer. A profile generation model (PGM) automatically determines the correct ion composition by rejecting all ion compositions with calculated values of three exact masses and two relative abundances that are inconsistent with the measured values. Knowledge of the molecular and fragment ion compositions in a mass spectrum constrains the number of possible isomers and can lead to compound identification based on modest library searches.